1. Field of the Invention
The subject invention provides an electrophysiological measure of the presence of cochlear hydrops in patients suspected of Meniere's disease.
2. Background
The major clinical diagnostic indicator of cochlear hydrops is hearing history. Cochlear hydrops is suspected if there is a fluctuating low-frequency hearing loss. Other popular older tests that have produced results of varying success are the glycerol test, the SP/AP (Summating Potential amplitude to compound Action Potential amplitude ratio) in electrocochleographic recordings, and, more recently, measures of cochlear traveling-wave velocities from derived-band Auditory Brainstem Responses (ABRs). Variations and combinations of these measures have also been investigated.
The disadvantages of the currently used diagnostic methods include:                (1) A fluctuating low-frequency hearing loss can occur in the absence of cochlear hydrops.        (2) The glycerol test is not an independent test because it must rely on another measure, (e.g., the SP/AP ratio) to determine if it is positive. Thus, the test is only as good as the second test used to measure the change that occurs due to administration of glycerol. Moreover, if the glycerol is administered orally, it is extremely unpleasant for the patient, and if administered intravenously it becomes an invasive procedure.        (3) The SP/AP ratio has been studied for a number of years and the results have varied greatly. Depending on the study, the sensitivity of the measure ranges from 50% and up. Other studies claim that the ratio change is due to changes in the AP value, whereas theoretically, changes due to cochlear hydrops should be in the SP value. While many studies can show a statistically significant difference for group or population data, the confidence of the diagnosis for a given individual is low due to overlap in the ratios for cochlear hydrops and non-hydrops populations. Moreover, the SP/AP ratio measures may require invasive transtympanic (needle through the eardrum) procedures for clear recordings. Even with transtympanic electrodes, due to the location of the recording electrode, these recordings are dominated by activity at the high-frequency end of the cochlea, whereas the diagnostic changes are more related to the low-frequency end of the cochlea.        (4) The cochlear traveling wave measures have not been studied extensively and their sensitivity and specificity are unknown at this time. Also, these measures have been shown to be highly variable across individuals because other factors unrelated to the presence of cochlear hydrops may affect these measures. We are currently investigating this measure in an NIH-funded grant project.        